Iron ore often contains considerable amounts of silicates. The presence of silicates has a detrimental effect on the quality of the iron, and it is therefore essential that the silicate content of the iron mineral can be considerably reduced. A common process of removing silicates from iron ore is reversed froth flotation, where the silicates are enriched in the flotate and leave the system with the froth, and the iron ends up in the bottom fraction.
After a reverse froth flotation step, generally the iron ore bottom fraction either contains a low level of silica but exhibits a low recovery of iron, or it exhibits high recovery of iron but contains a high level of silica. Various solutions have been proposed in the prior art to increase iron recovery and at the same time reduce silica levels. Very often these solutions have involved grinding the ores to fine particles.
When the ore has to be very finely ground to reach enough liberation of the minerals a problem can occur with the froth structure in the flotation. Fine particles may have impact on both generation of froth volume and stabilisation of the froth. The latter very often give problems when handling the froth product, both in the process as well as in reclaiming the water in thickeners.
In many cases it is desired to improve the recovery of iron by further processing of the froth product. Especially when the separated particles in the froth contain a high degree of mixed grains, it is possible to recover more iron. Additional grinding of froth product to increase liberation of iron ore is used, and if magnetite ore is processed, then additional magnetic separation may be performed. These processes are hampered by high amounts of froth.
When recovering water by using tailing thickeners, it is desired to have clear water leaving the top surface of the thickener. If there is a lot of froth on the surface there will be a contamination of the purified water, and high amounts of tailing products will return to the process. That will have a negative effect on the overall process, for example it will give rise to froth formation in magnetic separators, classifiers etc and bring back contaminants into the process. Finally, it can be mentioned that high amounts of froth will create a bottle neck in the process, as it will limit the maximum feed of ore to be processed.
Grinding (also referred to as milling) is an important step of the flotation process, which step is necessary to liberate the valuable species in the ore. The particle size to which an ore must be size-reduced in order to liberate the mineral values from associated gangue or non-values is called the liberation size, and this will vary from ore to ore. Initial examination of the ore should be made to determine the degree of liberation in terms of particle size in order to estimate the required fineness of grind. Test work should then be carried out over a range of grinding sizes in conjunction with flotation tests in order to determine the optimum mesh of grind.
In order to describe the distribution of particle sizes in an ore, the K80 value is generally used. The factor K80 is defined as the sieve opening through which 80% by weight of the material of the mineral sample passes. For example, if an ore has a K80 value of 75 μm, this means that 80% by weight of the material in the mineral sample will pass through a 75 μm sieve, and thus 20% by weight of the material of the sample will consist of particles having a diameter that is larger than 75 μm. The maximum K80 value from a mineralogical point of view is determined by the milling needed to liberate the minerals. Thus, the less milling needed, the higher the value of K80.
U.S. Pat. No. 6,076,682 discloses a process for enriching iron mineral from a silicate-containing iron ore by carrying out a reverse froth flotation in the presence of a silicate collecting agent containing a combination of at least one primary ether monoamine and at least one primary ether polyamine, where each of the ether amines contains an aliphatic hydrocarbyl group having 6-22 carbon atoms and the weight ratio of ether monoamine to ether polyamine is 1:4-4:1; and a depressing agent for the iron mineral. The working examples were performed with an iron ore having a K80 of about 75 μm.
SE 421 177 discloses a way to enrich oxidic minerals, especially iron minerals, by separation of silicate-containing gangues by foam flotation using a collector that is a combination of C8-C24 alkyl, preferably C10-C16 alkyl, fatty amines (mono-, di- or polyamines) and C8-C24 alkyl, preferably C8-C14-alkyl, ether diamines. The weight ratio of ether diamine to fatty amine is defined to be larger than 1.1:1. The K80 for the iron ore used in the working examples of this patent publication is 85 μm.
CA-A1-2 205 886 relates to compositions of matter comprising a blend of (a) an amine component, which is one or more compounds selected from the group consisting of alkyl amines, alkyl diamines, alkyl polyamines, ether amines and ether polyamines and mixtures thereof; and (b) a C3-C24 carboxylic acid or mixtures thereof; for use e.g. in the froth flotation of silica from iron ore. This patent publication is silent about the K80-value of the mineral samples flotated.
WO 2008/077849 relates to a reverse froth flotation process for removal of silicates from iron ore having K80≧110 μm using formulations comprising a C12-C15 alkyl ether diamine and a C12-C24 alkyl ether monoamine, a C12-C24 alkylamine or a C16-C24 alkyl diamine, wherein the weight ratio between the alkyl ether diamine and the other amine components is 1:5 to 5:1.
However, there still exists a need for collectors, with which reverse froth flotation of silicate-containing iron ore can be performed, that results in reduced froth formation and/or reduced froth stability.